An electronic component called an autofocus camera module is used in the camera lens part of a cellular phone. The autofocus function of the camera of the cellular phone unidirectionally moves the lens by the spring force of the material used in the autofocus camera module, and on the other hand, it moves the lens in a direction opposite to the direction in which the spring force of the material works, by an electromagnetic force generated by applying current to the coil wound around the periphery. Such a mechanism activates the camera lens thereby exhibiting the autofocus function (For example, patent literatures 1 and 2).
Thus, the strength enough to withstand the material deformation caused by electromagnetic force is required in the copper alloy foil used in the autofocus camera module. If the strength is low, it will not be possible for the material to withstand the displacement caused by electromagnetic force, thereby causing permanent deformation (settling). If settling occurs, it will not be possible to move the lens to a desired position when applying a certain current; and thus autofocus function is not exhibited.
The autofocus camera module uses a Cu—Ni—Sn based copper alloy foil having a foil thickness of 0.1 mm or less and a 0.2% yield strength of 1000 MPa or more. However, in response to the demand for recent cost cutting, a titanium copper foil whose material price is relatively cheaper than the Cu—Ni—Sn based copper alloy foil is being used and its demand is increasing.
However, the titanium copper foil has a lower strength than the Cu—Ni—Sn based copper alloy foil and causes a problem of settling; and therefore, higher strength is desired. To acquire a high strength titanium copper foil suitable for the autofocus camera module, various methods have been proposed. In patent literature 3, the method of controlling surface roughness of the copper alloy foil by sequentially performing hot and cold rolling, and then solution treatment, cold rolling with 55% or more rolling reduction, aging at 200 to 450° C., and cold rolling with 35% or more rolling reduction; and in patent literature 4, the method of controlling I(220)/I(311) by sequentially performing hot and cold rolling, solution treatment, cold rolling with 55% or more rolling reduction, aging at 200 to 450° C., cold rolling with 50% or more rolling reduction, and stress relief annealing as necessary to control the rolling reduction of cold rolling after solutionizing. Patent literatures 3 and 4 describes titanium copper foil which can achieve a 0.2% yield strength of 1100 MPa or more in the direction parallel to the rolling direction.
On the other hand, bending might be applied to the copper alloy foil used in the autofocus camera module. In this case, the copper alloy foil is required to have not only a high strength but also an excellent bending workability. As a measure to improve the strength and the bending workability of the titanium copper, various methods have been proposed, i.e., in patent literature 5, the method of performing hot rolling, cold rolling, and solution treatment, and then sequentially performing cold rolling before aging, aging treatment, and cold rolling after aging to set the rolling reduction after aging to 3% or more and the total rolling reduction of the cold rolling before and after aging to 15 to 50%, and in patent literature 6, the method of controlling half-value width of an X-ray diffraction intensity peak for {220} plane by performing hot rolling, cold rolling, and solution treatment, and then sequentially performing aging treatment, cold rolling with 40% or less rolling reduction, and stress relief annealing.